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Reactivity 2.3 Flashcards

Active Recall for Equilibrium

Flashcards: read all 10 questions and answers
  1. Define dynamic equilibrium.
    A state in a closed system where the rates of the forward and reverse reactions are equal, so macroscopic properties remain constant while reactions continue at the molecular level.
  2. State the two conditions for dynamic equilibrium.
    1. The system must be closed (no substances enter or leave). 2. The rate of the forward reaction equals the rate of the reverse reaction.
  3. State Le Chatelier's Principle.
    When a system at equilibrium is disturbed, it shifts in the direction that counteracts the change and partially restores the original conditions.
  4. Effect of increasing concentration of a reactant?
    Equilibrium shifts to the RIGHT (towards products) to use up the added reactant. K does not change.
  5. Effect of increasing temperature on an exothermic forward reaction?
    Equilibrium shifts LEFT (towards reactants = endothermic direction). K DECREASES.
  6. Does a catalyst change the position of equilibrium?
    No. A catalyst increases the rate of BOTH forward and reverse reactions equally. Equilibrium is reached faster, but the position (and K) is unchanged.
  7. Write the \(K_{\text{c}}\) expression for N₂(g) + 3H₂(g) ⇌ 2NH₃(g).
    \(K_{\text{c}} = \frac{[\text{NH}_3]^2}{[\text{N}_2][\text{H}_2]^3}\). Only temperature changes the numerical value of \(K_{\text{c}}\).
  8. What does a large K value mean?
    Products are strongly favoured at equilibrium - the equilibrium lies to the right.
  9. What is the difference between \(K_{\text{c}}\) and \(K_{\text{p}}\) ? (HL)
    \(K_{\text{c}}\) uses equilibrium concentrations (mol dm⁻³). \(K_{\text{p}}\) uses equilibrium partial pressures (for gaseous equilibria only).
  10. How do you calculate partial pressure? (HL)
    p_A = x_A × P_total, where x_A = mole fraction = n_A / n_total.
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